The present invention relates to a method of and means for enabling or controlling a reaction between particulate material and a reactant in a fluid medium in which said material is immersed. The reactions with which the invention may be concerned include chemical and biological processes and more generally may be any kind of process which relies on intimate mixing of two or more agents, one or both of which may be in particulate form, to effect some action between the agents.
When a material in particulate form is put in contact with another substance to undergo a chemical reaction, the efficiency of the reaction may be limited by the difficulty of ensuring that the particles are fully exposed to the reactant. Particularly if the product of the reaction is itself a solid, without special measures to prevent it acting as a barrier it may be possible to expose and react only a small proportion of the particulate material.
Mechanical stirring and agitating procedures are used to promote mixing, of course, and in recent years fluidised beds have been used to generate more intense reaction processes, but these known methods have a number of disadvantages and limitations. For example, although an object may be to obtain relative displacement between the particulate material and the fluid, if agitation of the particles is applied through the fluid the efficiency of mixing is limited, especially with mechanical mixing methods. To the extent that gravitational forces play any part, these are relatively weak and cannot be controlled; indeed their effects are dependent on the densities of the materials being processed. In the case of fluidised beds, moreover a minimum bed thickness is needed which can lead to clumping of the particulate matter even though a better mixing can be obtained than by mechanical methods.